The fabrication of magnetic tunnel junctions (MTJs), and, in particular, patterning and hard mask over-etching processes relating to the formation of MTJs, remains a challenge in forming magnetoresistive random access memory (MRAM) integrated circuits, especially concerning smaller MTJs, such as sub-micron and sub-100 nanometer (nm) MTJs. Patterning of MTJs often requires a self-aligned hard mask. The MTJ is typically formed and electrically coupled to an overlying metal interconnect by depositing a relatively thick metallic hard mask layer on top of the many layers of magnetic and nonmagnetic materials that will make up the MTJ. This hard mask layer is patterned into a desired shape by conventional photolithography and reactive ion etching (RIE). The MTJ layers are then patterned using the hard mask layer as a self-aligned mask structure. Afterwards, an interlayer dielectric (ILD) layer is deposited on the structure and polished so that it has a flat upper surface. Conventional photolithography and RIE are then used again to pattern a trench into the ILD layer in the shape of a desired interconnect feature. The trench is formed such that the thick hard mask layer protrudes into the trench. Finally, the trench is filled with a metallic material in order to form the interconnect feature. The thick hard mask layer therefore serves as both an etch mask and a contact that connects the MTJ to the top electrode. Hence, the hard mask needs to be patterned cleanly. More importantly, the patterning of the hard mask needs to be done in a manner that is benign to the magnetic stack.
Unfortunately, in current MTJ fabrication approaches, a photoresist strip step that conventionally follows the hard mask over-etch step often leaves behind a photoresist spine. Furthermore, the photoresist strip after the hard mask over-etch process leads to an etching into the magnetic stack and results in a non-uniform field area and unknown thickness, which is undesirable.